The present invention relates to the field of product manufacturing, and, more particularly, to manufacturing of semiconductor wafers.
Manufacturing Information Systems (MISs) are systems that contain data and data processing methods that aid manufacturing managers in production planning and execution. For example, an MIS typically contains demand data, supply data, cost data, and bill-of-material data. Manufacturing Resource Planning (MRP), Capacity Requirements Planning (CRP) and Enterprise Resource Planning (ERP) are types of MISs. An MIS is primarily a data management system. Most important manufacturing decisions are still ultimately made by humans; however, software that processes all the relevant data and uses mathematical techniques to determine optimal, feasible production plans can save millions of dollars for manufacturers.
ERPs may track and manage a multi-profile workforce, process attendance parameters, allocate actual cost records, optimize resource utilization and measure labor productivity throughout the enterprise. Furthermore, workplace logistics, production planning, material management, sales, project accounting, human resources and payroll may also be managed with such systems.
Semiconductor devices, also called integrated circuits, are manufactured and mass produced by fabricating identical circuit patterns on a single semiconductor wafer. During the process, the wafer is cut into identical dies or chips. Although commonly referred to as semiconductor devices, the devices are fabricated from various materials, including conductors (e.g. copper, aluminum and tungsten), non-conductors (e.g. silicon dioxide) and semiconductors (e.g. silicon). Within an integrated circuit, thousands of devices (e.g., transistors, diodes) are formed.
In a semiconductor fabrication plant (fab), the integrated circuit devices with their various conductive layers, semiconductive layers, insulating layers, contacts and interconnects are formed by fabrication processes, including doping processes, deposition processes, photolithographic processes, etching processes and other processes. Many operators are needed at various process stations (e.g. a group of machines) in the fab to sustain a given production volume.
For example, U.S. Pat. No. 5,140,537 to Tullis and entitled xe2x80x9cModeling as Factory with Human Operators and Validating the Modelxe2x80x9d is directed to a computer simulation of a semiconductor factory. The simulation includes comparatively evaluating individual lots as they move through process sequences over time. Historical records of staffing are used to determine staff levels to include in the model.
Additionally, a typical semiconductor fab includes a lot tracking system. A lot is a group of wafers which are typically processed together. Computer software running on a local area network is used to collect data regarding product flow in order to keep track of individual and groups of lots as they move through the processing stations in a work center. For example, AccuFACTS 9000 from Santa Barbara Analysis, Inc., of Valencia, Cal. is a shop floor lot tracking software product which collects real time data regarding works in progress, lot locations and processing station inventory, for example.
Typically, in the semiconductor manufacturing industry, the number of operators needed is calculated through the use of time studies. Such time studies are based on the detailed observation of all the operators activities, the classification of the activities, and the measurement or estimation of the time needed to perform all of them. These studies are very slow and expensive, and they are discontinuous and thus do not provide frequent or accurate tracking of manpower.
In view of the foregoing background, it is therefore an object of the invention to provide a method and system for quickly and continuously determining a total number of operators needed at a work center to achieve a manufacturing goal.
This and other objects, features and advantages in accordance with the present invention are provided by a method of determining a total number of operators needed at a semiconductor wafer work center to achieve a wafer manufacturing goal. The work center includes a wafer lot tracking system and a plurality of processing stations for processing a plurality of lots of semiconductor wafers to be manufactured. The method includes the steps of setting the wafer manufacturing goal, determining a highest operator throughput as a maximum rate of wafers that can be processed per operator based on data from the lot tracking system, and determining a minimum number of operators that are needed to process wafers in the work center to achieve the manufacturing goal based on the wafer manufacturing goal and the highest operator throughput.
The method further includes the determination of a number of working operators needed to process wafers in the semiconductor wafer work center to achieve the wafer manufacturing goal by increasing the minimum number of operators based on characteristics of the processing stations. An operator availability based on an average number of working operators and a number of all operators at the work center is also determined. The total number of operators needed at the semiconductor wafer work center to achieve the wafer manufacturing goal is then determined based on the operator availability and the number of working operators.
The step of determining the total number of operators needed at the semiconductor wafer work center to achieve the wafer manufacturing goal may also be based on a work center operating time and a working time per operator. Also, the step of determining the total number of operators needed at the semiconductor wafer work center to achieve the wafer manufacturing goal may comprise multiplying the quotient of the number of working operators needed divided by the operator availability, by the quotient of the work center operating time divided by the working time per operator. The step of setting the wafer manufacturing goal may be based on a rate of wafers that can be started in a product flow and a number of process steps in the product flow.
Additionally, the step of determining the number of working operators may comprise dividing the minimum number of operators by an operator cushion. The operator cushion is preferably between 0 and 1 and may be a historical factor. The step of determining the minimum number of operators may comprise dividing the wafer manufacturing goal by the highest operator throughput. Also, the step of determining the operator availability may comprise dividing the average number of working operators by the number of all operators at the work center.
The objects, features and advantages in accordance with the present invention are also provided by a system for determining a total number of operators needed at a semiconductor wafer work center to achieve a wafer manufacturing goal. Again, the work center includes a wafer lot tracking system and a plurality of processing stations for processing a plurality of lots of semiconductor wafers to be manufactured. The system includes means for determining a highest operator throughput as a maximum rate of wafers that can be processed per operator based on data from the lot tracking system, and means for determining a minimum number of operators that are needed to process wafers in the work center to achieve the manufacturing goal based on the wafer manufacturing goal and the highest operator throughput.
The system also includes means for determining a number of working operators that are needed to process wafers in the work center to achieve the wafer manufacturing goal by increasing the minimum number of operators based on characteristics of the processing stations, and means for determining an operator availability based on an average number of working operators and a number of all operators at the work center. Furthermore, the system includes means for determining the total number of operators needed at the semiconductor wafer work center to achieve the wafer manufacturing goal based on the operator availability and the number of working operators.
The means for determining the total number of operators needed at the semiconductor work center to achieve the wafer manufacturing goal may also be based on a work center operating time and a working time per operator. The means for determining the total number of operators needed at the semiconductor work center to achieve the wafer manufacturing goal may be for multiplying the quotient of the number of working operators needed divided by the operator availability, by the quotient of the work center operating time divided by the working time per operator. Again, the wafer manufacturing goal may be based on a rate of wafers that can be started in a product flow and a number of process steps in the product flow.
The means for determining the number of working operators may be for dividing the minimum number of operators by an operator cushion. Again, the operator cushion is preferably between 0 and 1 and may be a historical factor. Also, the means for determining the minimum number of operators may be for dividing the wafer manufacturing goal by the highest operator throughput, and the means for determining the operator availability may be for dividing the average number of working operators by the number of all operators at the work center.